Архив научных статейиз журнала «Физиология растений»
ABSCISIC ACID ENHANCED AJMALICINE BIOSYNTHESIS IN HAIRY ROOTS OF RAUVOLFIA VERTICILLATA BY UP-REGULATING EXPRESSION OF THE MEP PATHWAY GENES
CHANG K., CHEN M., LAN X., LIAO Z., WANG Q., ZENG L. — 2014 г.
Hairy root cultures of Rauvolfia verticillata were established and used to analyze the expression of the eight ajmalicine-pathway genes (the five MEP pathway genes, including DXR, MCT, MECS, HDS, and HDR; the three ajmalicine-pathway-specific genes, including TDC, STR, and SGD) and ajmalicine accumulation in the cultures treated with ABA. In the ABA treatment, the five MEP-pathway genes were simultaneously up-regulated at the transcriptional level, while the three ajmalicine-pathway-specific genes, including TDC, STR, and SGD were not up-regulated. The statistical analysis showed that the MEP pathway gene expression levels in the ABA treatment were significantly different from those in the control. TDC showed no response to ABA treatment, and SGD expression decreased slightly. Surprisingly, the well-known rate-limiting enzyme gene STR showed dramatically decreased expression in the ABA treatment. The HPLC analysis showed that the content of ajmalicine in the ABA-treated hairy roots of R. verticillata (196.9 ± 3.6 dry wt) was significantly higher than that in the control (171.0 ± 7.6 dry wt). This suggests that the higher expression levels of the MEP pathway genes could enhance ajmalicine biosynthesis and the MEP pathway plays an important role in ajmalicine biosynthesis in R. verticillata. Finally, STR might not be the rate-limiting enzyme involved in ajmalicine biosynthesis of R. verticillata.
ANTIOXIDANT ENZYME RESPONSES TO SALINITY STRESS OF JATROPHA CURCAS AND J. CINEREA AT SEEDLING STAGE
ASCENCIO-VALLE F., ENDO T., FUJIYAMA H., HISHIDA M., LARRINAGA-MAYORAL J.A., ORDUNO-CRUZ A. — 2014 г.
The salt-sensitive humid tropical biodiesel crop, Jatropha curcas, was subjected to a 28-day exposure to salinity (0, 50, 100, and 200 mM NaCl), and activities of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX), the rate of lipid peroxidation, stomatal conductance, mineral contents, and chlorophyll (Chl) content were compared to corresponding characteristics of J. cinerea, a related wild species of saline-dry areas. Biomass production decreased under the influence of 50 mM NaCl in both species, and the reduction was larger in J. curcas than in J. cinerea at higher NaCl concentrations. In both species, stomatal conductance and transpiration decreased, and leaf temperature and Na+ concentration increased under salt treatment; salinity effect was stronger in J. curcas. Chl degradation enhanced only in J. curcas. In both Jatropha species, SOD, CAT, and POX activities increased with salinity. J. curcas showed higher antioxidant activity than J. cinerea. Lipid peroxidation was observed only in J. curcas at concentrations above 100 mM NaCl, partially due to a greater reduction in stomatal conductance and/or the poor ROS-scavenging system. Thus, J. cinerea had more favorable characteristics to adapt to saline environments, and young J. curcas plants could adapt to salt-affected land if soil salinity was moderate (about 50 mM NaCl in solution).
APYRASE, STREPTAVIDIN-BINDING PROTEIN, AND ANTIMICROBIAL ACTIVITY IN PISUM SATIVUM
MOUSTAFA M.F.M. — 2014 г.
The 49 kD apyrase (EC 188.8.131.52), streptavidin-binding protein, and antimicrobial activity in the subcellular fractions from different seed parts of Pisum sativum L. var. Alaska were examined. Except cotyledons, all subcellular fractions contained 49 kD apyrase, and a considerable relationship was found between 49 kD apyrase and NTPase activities that increased with increasing time of germination. The bulk of 49 kD apyrase and NTPase activities was found in the nucleus pellets and cytoskeleton-enriched fraction, indicating their physiological importance. At 72 h of germination, all subcellular fractions of primary stems have a greater amount of 49 kD apyrase and NTPase than primary leaves and much more than primary roots and cotyledonary stalks. All seed parts showed antimicrobial activities, and the bulk of inhibition activities was found in the cytoskeleton-enriched and nucleus pellets, which was greater in the primary stems and leaves than in other parts. Current findings reveal that apyrases have important roles in metabolic activities in all parts of the pea plants except cotyledons. Cotyledons contained much streptavidin-binding proteins, which might have different physiological roles than apyrases.
AUXIN REDISTRIBUTION AND SHIFTS IN PIN GENE EXPRESSION DURING ARABIDOPSIS GRAFTING
JIN Z., LIU H., MU C.J., REN Z.Z., WANG J., WANG M.Q., XU J., YAN B., YIN H., ZHANG Y. — 2014 г.
Auxin is important in the development of plant vascular tissues. Reconnection of vascular bundles between scion and stock is a primary aim of grafting, and polar auxin transport greatly affects the formation of a continuous vascular model. The role of auxin in the process of graft-union development was studied by grafting the seedlings of Arabidopsis thaliana Heynh. DR5:GUS marker plants, which exerts the auxin-specific responses. Auxin induced the DR5:GUS expression in the vascular bundles around graft surface and stimulated the formation of multiple vascular bundle reconnections on the third day after grafting (DAG). DR5:GUS expression was delayed for one day in both scion and stock and dramatically declined by the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA). Vascular bundle reconnection was observed only on the fourth DAG. These results suggest that auxin stimulates the reconnection of the vascular bundles, whereas NPA inhibits it. We studied the role of PIN proteins in graft development by grafting seedlings of PIN:GUS plants. PIN had different expression patterns in the graft process. Expression levels of PIN genes were analyzed by real-time PCR. All PIN genes had the higher expression level at the third DAG. We conclude that auxin stimulates the development of graft unions, and the patterns of expressions of PIN family genes can affect the development of graft union by controlling the auxin flow.
AZIDE-DEPENDENT NITRIC OXIDE EMISSION FROM THE WATER FERN AZOLLA PINNATA
COHEN M.F., GURUNG S., YAMASAKI H. — 2014 г.
Nitric oxide (NO) is involved in versatile functions in plant growth and development as a signaling molecule. To date, plants have been reported to produce NO following exposure to nitrite (NO ), the amino acid L-arginine, hydroxylamine, or polyamines. Here we demonstrate azide-dependent NO production in plants. The water fern Azolla pinnata emitted NO into air upon exposure to sodium azide (NaN3). The NO production was dependent on azide concentration and was strongly inhibited by potassium cyanide (KCN). Incubation of A. pinnata with the catalase inhibitor 3-aminotriazole (3-AT) abolished the azide-dependent NO production. Although nitrite-dependent NO production was inhibited by sodium azide, azide-dependent NO production was not affected by nitrite. These results indicate that A. pinnata enzymatically produces NO using azide as a substrate. We suggest that plants are also capable of producing NO from azide by the action of catalase as previously reported in animals.
CHARACTERISTICS OF BIOENERGY GRASSES IMPORTANT FOR ENHANCED NACL TOLERANCE POTENTIAL
CHANDRAN S., MIRSHAD P.P., PUTHUR J.T. — 2014 г.
Growing bioenergy grasses can contribute to a great extent towards the production of biomass, and it can be a potential source of renewable energy. Such grasses, if suitable for marginal land, will solve better the problem of its competition with the cultivation of food crops in arable land. Four different potential bioenergy grasses, e.g., Saccharum arundinaceum Retz., hybrid Napier var. CO-3, Saccharum spontaneum L., and Arundo donax L. were selected based on our earlier study, and these perennial grasses were subjected to NaCl stress, a characteristic feature of marginal lands. Various measurements to assess the NaCl tolerance mechanism, e.g., MDA content, antioxidant enzyme activity, photosynthetic pigments composition, chlorophyll fluorescence and photosystem I (PSI) and photosystem II (PSII) activities were analyzed after imparting NaCl stress and compared with the control plants. Among the grasses studied, a lower maximum quantum yield of PSII (Fv/Fm) and PSI and PSII activities were recorded in S. spontaneum and Napier var. CO-3 than in S. arundinaceum and A. donax. The latter two grasses showed less degradation of total chlorophyll and low MDA content. The maintenance of a better water status of A. donax and S. arundinaceum is attributed to the maintenance of favorable osmotic balance by the accumulation of the higher levels of compatible solutes, such as total soluble sugars and proline. The better performance of S. arundinaceum and A. donax under high NaCl conditions was also facilitated by the higher free radical-scavenging potential in them, as represented by the increase in peroxidase activity. These results suggest that S. arundinaceum and A. donax are better adapted to NaCl stress than S. spontaneum and Napier var. CO-3. The high NaCl tolerance potential, exhibited by S. arundinaceum and A. donax, makes them an appropriate choice for marginal lands affected by high levels of NaCl.
CHARACTERIZATION OF PROTEASES SECRETED BY LEEK ROOTS
ADAMCZYK B. — 2014 г.
Some characteristics of root-secreted proteases were studied. We measured their molecular weights and mechanism of BSA digestion in comparison to endogenous root proteases. We related these studies to culture medium N composition. The seedlings of Allium porrum L. (cv. Bartek) were cultivated on MS medium, MS without inorganic nitrogen (MS-IN), and MS without IN, but with 0.1% casein (MS-IN + 0.1% casein). Electrophoretic study showed that root-secreted proteases had one isoform with a mol wt of 45 kD, regardless of medium N composition. Difference in molecular weights of root-secreted proteases and endogenous root proteases active under used conditions (>66 kD) provide us another strong evidence that root-secreted proteases were not just leaking from the roots, but they were secreted. Proteases exuded by roots degraded BSA in a similar way as endogenous proteases, with only one SDS-PAGE-detectable product of degradation. Our results may be a powerful tool in the extraction and purification of these enzymes and also in proteomic studies.
CLONING AND CHARACTERIZATION OF PATHOGENESIS-RELATED PROTEIN 4 GENE FROM PANAX GINSENG
JANG M.G., KIM S.Y., KIM Y.J., KWON W.S., LEE H.J., YANG D.C. — 2014 г.
The family of pathogenesis-related protein 4 (PR4) is a group of proteins with a Barwin domain in C-terminus and generally thought to be involved in plant defense responses. In the present study, PR4 (designated as PgPR4) cDNA was isolated from the leaf of Panax ginseng C.A. Meyer and characterized. The ORF is 513 bp with a deduced amino acid sequence of 170 residues. A GenBank BlastX search revealed that the deduced amino acid of PgPR4 shares the highest sequence similarity to PR4 of Sambucus nigra (72% identity). Sequence and structural analysis indicated that PgPR4 belongs to class II of PR4 proteins. This is the first report on the isolation of PR4 gene from the P. ginseng genome. The high-level expression of PgPR4 was observed in the root as revealed by quantitative real-time PCR. The temporal expression analysis demonstrated that PgPR4 expression could be up-regulated by pathogen infection, salt, wounding, and hormone stresses. These results suggest that PgPR4 could play a role in the molecular defense response of ginseng to abiotic stress and pathogen attack.
CLONING AND CHARACTERIZATION OF URIDINE DIPHOSPHATE GLUCOSE DEHYDROGENASE GENE FROM IPOMOEA BATATAS
GU Y.H., LAI X.J., TAO X., WANG H.Y., ZHANG Y.Z. — 2014 г.
In order to study the structure and expression patterns of uridine diphosphate glucose dehydrogenase (UDPGH) genes in Ipomoea batatas, the transcriptome database of this plant constructed in our lab was first analyzed to screen UDPGH contigs. It was found that there were 23 UDPGH contigs of different sizes in the transcriptome database. Primers were designed to amplify the coding regions of UDPGH, and five UDPGH-coding genes (named IbUDPGH1IbUDPGH5) were cloned and sequenced. Open reading frames of all the UDPGH were 1443 bp in length, and their identity was more than 97 and 99% at the nucleotide and protein level, respectively. Homology comparison among different plant UDPGH showed that the identity ranged from 73 to 85% at the nucleotide level and from 84 to 95% at the protein level. The results of digital gene expression profile analysis (DGE) displayed that IbUDPGH1 had the highest expression in the tuberous roots, lower in the young and mature leaves, and the lowest in stems and fibrous roots, while IbUDPGH2 and IbUDPGH5 had the highest transcript level in stems, lower in roots, and very low in leaves. The rest genes were expressed at a low level in different tissues. Semi-quantitative RT-PCR results were similar to above data from the DGE. These results imply that the high expression of UDPGH might make large contribution to the accumulation of cell wall polysaccharides of sweet potato stems and roots.
CLONING AND EXPRESSION PROFILE OF 1-DEOXY-D-XYLULOSE 5-PHOSPHATE REDUCTOISOMERASE GENE FROM AN OIL-BEARING ROSE
WANG H., YAO L. — 2014 г.
The components of rose essential oil are mainly monoterpene alcohols, predominantly synthesized through the methylerythritol 4-phosphate (MEP) pathway in plants. 1-Deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) is specified to be a first committed enzyme of the MEP pathway. In order to understand better the role of DXR in the rose essential oil biosynthesis at the molecular level, the full-length cDNA of DXR sequence (designated as RhDXR) was isolated from an oil-bearing rose hybrid Rosa cv. Zizhi and characterized, and the expression profile of it was investigated. Essential oils of rose Zizhi and the other five oil-bearing roses were distilled to evaluate the relationship between the expression of DXR gene and oil yield rate. The full-length cDNA of RhDXR was 1915 bp in length, comprised an open reading frame of 1419 bp, encoding an enzyme of 472 amino acids. A comparative analysis with DXRs of selected species from bacteria to higher plants revealed three conserved domains: a conserved cleavage site for plastids, an extended Pro-rich region, and a highly conserved NADPH oxidase-binding motif existing in the N-terminal region, like in other higher plant species. The relative expression levels of the DXR gene were determined in various tissues: the receptacle, leaf, sepal, pistil, stamen, and petal (in the order of decreasing expression level), and at different flowering stages (flower bud, flower in half bloom and full bloom). Six cultivars could be classified into two groups according to flower color, and within each group there was a positive correlation between the expression level of DXR gene and oil yield rate.
CLONING AND EXPRESSION PROFILE OF BETAINE ALDEHYDE DEHYDROGENASE GENE OF IPOMOEA BATATAS IN RESPONSE TO SALT STRESS
CHEN J., JIANG Y.S., TAN X.M., TAO X., ZHANG Y. — 2014 г.
Betaine aldehyde dehydrogenase (BADH) is a key enzyme for glycine betaine synthesis, which plays an important role in improving plant tolerance to salinity. Until now, little is known about the molecular biology of BADH gene in sweet potato (Ipomoea batatas (L.) Lam.). Here, we report the cloning, sequencing, and expression of Ib-BADH gene of sweet potato. The sequencing results showed that Ib-BADH contains a 1509 bp open reading frame coding for a protein of 502 amino acid residues. It is also found that there are three highly homologous isoforms (identity >99%) of Ib-BADH in sweet potato. The results from both digital gene expression profiling and semi-quantitative reverse transcriptionpolymerase chain reaction demonstrated that the expression levels of Ib-BADH were different among various tissues and development stages under natural condition and salt stress.
COMPUTATIONAL IDENTIFICATION OF MIRNA GENES AND THEIR TARGETS IN MULBERRY
HUANG Y., WANG Z.B., ZOU Q. — 2014 г.
MicroRNAs (miRNA) are a class of tiny non protein coding and regulatory RNA molecules about 18 to 26 nt in length. miRNA regulate gene expression via the degradation or translational inhibition of their target mRNAs. Nucleotide sequences of miRNAs are highly conserved among various organisms; this forms the key feature behind the identification of miRNAs in plant species by homology alignment. So far, little is known about miRNA in mulberry (Morus alba L.) species. In our study, a computational method was used for detection of mulberry miRNAs. A total of six miRNAs were identified. The six miRNAs may regulate twenty-two potential targets, which are predicted to encode transcription factors that regulate plant development, signaling, and metabolism. To validate the prediction of miRNAs in mulberry, a RT-PCR experimental method was performed and five of these miRNAs were found to be expressed.
DEVELOPMENT OF TYLOSES IN THE XYLEM VESSELS OF MEILI GRAPEVINE AND THEIR EFFECT ON WATER TRANSPORTATION
LI H., LIU L.Y., NAN L.J., WANG H., ZHAO X.H. — 2014 г.
Shoot pruning could cause short-term damages to vines. In response to damage, tyloses develop in shoot xylem vessels interfering free water and mineral transportation. In this study, the tylosis development at different nodes of the current-year and perennial shoots of sixty three-year-old grapevines (Vitis vinifera L.) after pruning was investigated. The results showed that tyloses at the nodes closest to the trunk developed rapidly; and tylosis development initiated at the time when the size of vessel-ray pit was greater than that of parenchyma cell-parenchyma cell pit. In current-year shoots, tyloses were formed in up to 87% of the vessels, and 40% of the vessels were completely blocked by tyloses. In wound-induced perennial shoots, 30% of the vessels were completely blocked by tyloses. When few vessels were blocked by tyloses, new vessels could differentiate, and water transportation system may be restored. However, when tyloses developed in a large number of vessels and the large number of the vessels were blocked, the original capability of water transport was decreased (the largest decrease was 21.1% in this study), resulting in dehiscence or shrinkage cracking in this area. The study proved that the tylosis formation in functional vessels limited the water transport efficiency.
DIFFERENCES IN PHYSIOLOGICAL CHARACTERISTICS BETWEEN TWO WHEAT CULTIVARS EXPOSED TO FIELD WATER DEFICIT CONDITIONS
GUO Q.F., LUO Y., TIAN F.X., WANG W., WU Y.L. — 2014 г.
We investigated various physiological characteristics of two wheat (Triticum aestivum L.) cultivars differing in drought tolerance, i.e., Shannong16 (a drought-tolerant cultivar) and Weimai8 (a high-yield wheat cultivar under well-watered conditions), under field drought conditions. The experiments were conducted over a two-year period. Drought stress (DS) was imposed by controlling irrigation and sheltering the plants from rain. Compared with Weimai8, Shannong16 exhibited the better water balance, the higher osmotic adjustment, the slower degradation of chlorophyll, and the higher net photosynthetic rate under drought-stress conditions. At the same time, we observed that Shannong16 maintained more integrated chloroplast and thylakoid ultrastructure in flag leaves than Weimai8 under field drought stress. The different levels of antioxidant competence, indicated by MDA content, antioxidant enzyme activities, and the level of superoxide radicals observed in the two wheat cultivars may be involved in the different levels of drought resistance of these cultivars.
EFFECT OF EXOGENOUS POTASSIUM ON PHOTOSYNTHESIS AND ANTIOXIDANT ENZYMES OF RICE UNDER IRON TOXICITY
GAO P.P., LIU P., WU Y.H., ZHENG G.H. — 2014 г.
A solution culture experiment was conducted to determine the effects of different potassium concentrations on the chlorophyll fluorescence and oxidation resistance of the Fe2+-tolerant rice (Oryza sativa L.) genotype Xieyou 9308 and the Fe2+-sensitive genotype IIyou 838 exposed to 250 mg/L of Fe2+. The minimal fluorescence, maximum fluorescence efficiency, maximum fluorescence, and non-photochemical quenching coefficient showed no significant changes. However, the photochemical quenching coefficient increased. Under 200 mg/L K+ concentration, the effects of Fe2+ stress decreased. Compared with the control group, chlorophyll content and peroxidase, superoxide dismutase, and catalase activities decreased, whereas MDA content increased under Fe2+ stress. Exogenous K+ alleviated Fe2+ toxicity in the test subjects compared with the control group. Overall, external K+ could alleviate the toxic effects of Fe2+ toxicity.
EFFECT OF LOW DOSE OF SPERMIDINE ON PHYSIOLOGICAL CHANGES IN SALT-STRESSED CUCUMBER PLANTS
LEE I.J., RADHAKRISHNAN R. — 2014 г.
The present study was aimed to assess the ameliorative potentiality of exogenously applied low dose of spermidine (Spd) (4.0 mL of 0.1 mM) against salt stress in cucumber plants (Cucumis sativus L.). Salt stress inhibited plant growth, while Spd increased the shoot length and dry weight of leaves in salt-stressed plants. Chlorophyll, carotenoids, and sucrose contents were lower, and the accumulation of superoxide radical was higher in salt-affected plants than in controls, and these detrimental effects were mitigated by Spd treatment. Moreover, salinity diminished the reduced glutathione and total polyphenols and inhibited the activities of catalase, peroxidase, and polyphenol oxidase as compared with controls, and Spd treatment increased all antioxidant activities in salt-injured plants. NaCl-induced oxidative stress caused a significant decrease in GA4 and GA5 contents. Spd treatment ameliorated these salt stress effects by increasing the quantities of GA4. In addition, sodium content was higher and calcium content was lower in salt-treated plants, while Spd treatment reduced the sodium accumulation and increased the calcium level in plants exposed to NaCl. The results suggest that exogenous application of low Spd dose can ameliorate the salt stress effects on cucumber by modulating the components of photosynthetic pigments, antioxidants, gibberellins, and minerals.
EFFECT OF SALICYLIC ACID PRETREATMENT ON DROUGHT STRESS RESPONSES OF ZOYSIAGRASS (ZOYSIA JAPONICA)
CHEN Z.L., LI X.M., ZHANG L.H. — 2014 г.
The present study was carried out to examine the effects of exogenous salicylic acid (SA) on growth, activities of antioxidant enzymes, and some physiological and biochemical characteristics of zoysiagrass (Zoysia japonica Steud.) plants subjected to drought. Aqueous 0.1, 0.5, or 1.0 mM SA solution was sprayed on the leaves of zoysiagrass for 3 days. Drought was induced by withholding watering for 16 days after SA application. Biomass, chlorophyll content, net photosynthetic rate (Pn), activities of antioxidant enzymes (e.g., superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), MDA and proline contents were determined. Pretreatments with 0.1 and 0.5 mM SA significantly increased fresh and dry weights and chlorophyll content, while 1 mM SA pretreatment did not show significant change compared to controls. SA pretreatments showed a marked increase in Pn compared with controls from the 7th to 16th day after drought start. Activities of SOD, POD, and CAT were increased by SA pretreatments. MDA and proline contents after 0.1 and 0.5 mM pretreatments were lower than those of controls from the 6th to 12th day of drought, while 1 mM SA pretreatment did not show significant change from the 0th to 9th day of drought. This work suggests that suitable exogenous SA (0.5 mM) helps zoysiagrass to perform better under drought stress by enhancing the net photosynthetic rate and antioxidant enzyme activities while decreasing lipid peroxidation as compared to the controls. SA could be used as a potential growth regulator for improving plant growth under drought stress.
EFFECT OF TIO2 NANOPARTICLES ON OXIDATIVE DAMAGE AND ANTIOXIDANT DEFENSE SYSTEMS IN CHICKPEA SEEDLINGS DURING COLD STRESS
MAALI-AMIRI R., MANTRI N.L., MOHAMMADI R. — 2014 г.
The effects of TiO2 nanoparticles (NPs) on physiologo-biochemical responses were studied in two chickpea (Cicer arietimun L.) genotypes differing in cold sensitivity (tolerant Sel11439 and sensitive ILC533) during cold stress (CS). The results showed that hydrogen peroxide and MDA contents and electrolyte leakage index (ELI) increased under CS conditions in both genotypes and that these damage indices were higher in ILC533 than in Sel11439 plants. In plants treated with TiO2 NPs, a decreased H2O2 level was accompanied by a decrease in the MDA content and ELI compared to control plants, and these changes occurred more effectively in Sel11439 than in ILC533 plants. The antioxidant enzymes were more effective in cell protection against CS in Sel11439 plants compared to ILC533 plants, as well as in plants treated with TiO2 NPs compared to control plants. The lipoxygenase activity was induced efficiently only in Sel11439 plants treated with TiO2 NPs during CS, probably indicating its role in stress response (which was confirmed by measuring allen oxide synthase activity). TiO2 NPs caused stability of chlorophyll and carotenoid contents during CS. Results suggest that TiO2 NPs confer an increased tolerance of chickpea plants to CS, decreasing the level of injuries and increasing the capacity of defense systems.
EFFECTS OF POTASSIUM DEFICIENCY AND REPLACEMENT OF POTASSIUM BY SODIUM ON SUGAR BEET PLANTS
GENG G., GUO X.L., KONG X.S., PENG C.X., PI Z., STEVANATO P., YANG Y., YV L.H. — 2014 г.
Two sugar beet (Beta vulgaris L.) genotypes were cultivated at different K+/Na+ concentration nutrient solutions (mM, 3.00/0 (control groups), 0.03/2.97 (K-Na replacement groups), and 0.03/0 (K deficiency groups)) to investigate the effects of potassium deficiency and replacement of potassium by sodium on plant growth and to explore how sodium can compensate for a lack of potassium. After 22 days of growth were determined: (i) dry weights of leaves, stems, and roots, (ii) the Na+ and K+ contents, (iii) MDA level, (iv) the activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX), and (v) the level of free amino acids. Potassium deficit inhibited plant growth, decreased the K+ content in leaves and roots, activated GPX and SOD, suppressed CAT activity, and increased the content of most amino acids. In K-Na replacement groups, the effects of K+ deficiency, including changes in the MDA level, antioxidant enzyme activities, and the level of free amino acids, were alleviated, but the degree of recovery did not reach the values characteristic for the control groups. Based on these results, we concluded that low potassium could lead to the inhibition of seedling growth, oxidative damage, and amino acid accumulation. While sodium was able to substitute potassium to a large extent, it cannot fulfil potassium fundamental role as an essential nutrient in sugar beet.
EFFECTS OF SILICON ON ZEA MAYS PLANTS EXPOSED TO WATER AND OXYGEN DEFICIENCY
GADALLAH M.A.A., SAYED S.A. — 2014 г.
Effects of shoot and root supplementation with silicon on the response of Zea mays L. plants to matric water potential ( m) and oxygen deficiency (waterlogging) stresses were studied. The soil water limitation ( m) and oxygen deprivation significantly reduced shoot dry weight, chlorophyll (Chl) content, ascorbic acid content, as well as leaf relative water content. Both soil drying and waterlogging caused a significant increase in the leaf membrane injury by heat (51°C) and dehydration (40% PEG) stresses. The levels of lipid peroxidation (POL) and hydrogen peroxide (H2O2) content were increased by excess soil drying and oxygen deficiency. Supplementary silicon at 1.0 mM significantly increased Chl content and improved water status. Concentrations of H2O2, MDA, and proline and leaf membrane injury were significantly reduced by Si application. The reverse helds true for ascorbic acid. The results of this study indicate that application of silicon might improve growth attributes, effectively mitigate the adverse effect of drought and waterlogging, and increase tolerance of maize plants. The silicon-induced improvement of drought and anoxia tolerance was associated with the increase in oxidative defense abilities.